Three dimensional fabrics are used in a wide variety of applications. U.S. Pat. No. 4,36,296 discloses a composite member having a core formed from a three dimensional fabric. As disclosed therein, the three dimensional fabric has a multiplicity of warp strings latticed in a plurality of columns and rows. First and second wefts are woven between the columns and rows of the warp strings. The three dimensional fabric forms the core of a composite member and is impregnated with a resin or inorganic material that gives the composite a great deal of strength. The described fabric can be used as a structural member in a wide variety of applications, including rockets, aircraft, automobiles, marine vessels and buildings. However, in order to make good use of the composites, it is desireable to provide a linkage mechanism for coupling the composite members to similar composites and/or other structural members. Such a linkage arrangement is not disclosed in the '296 patent.
In the past, linkages have been provided on composite materials having a laminated cloth cores. Referring to FIG. 36, a composite member 60 has a core formed from a multiplicity of laminated cloth pieces. A metallic bushing 61 multiplicity of laminated cloth pieces. A metallic bushing 61 is inserted into the laminated cloth based composite member 60. A bolt 63 and nut 64 are then used to couple the composite member 60 to structural member 62 or a second composite member.
An application of the same approach to three dimensional fabrics based materials requires that a hole be punched into the fabric in order to receive the metallic bushing. However, when a hole is formed in a composite member having a three dimensional fabric as its base, the fabric's strings are necessarily cut which significantly reduces the fabric's overall strength. Referring specifically to FIG. 37, the strength of fabric F having a hole 65 cut therein will be particularly weakened under the influence of forces in the direction of arrows 69. To compensate for the weaknesses induced by hole 65, the fabric must be enlarged by increasing its length and width. Furthermore, if the hole 65 is punched after a composite member has been formed, subtle cracks may be induced in the composite by the punching action. Such cracks create stress concentrations which weaken the composite member and make it extremely difficult to calculate a given member's actual strength.
Yet another prior art method of joining composite members is adhesive bonding. However, such an approach also has several drawbacks. For example, both the assembly and the disassembly of the members are relatively difficult. Further, the resulting bond strength can vary a great deal due to inherent variations in the bonding process.
Accordingly, there is a need for an improved mechanism for securing three dimensional fabrics and composite members having three dimensional fabric cores to other members, including both structural members (some of which may be metallic) and other composite members.